A retrospective study of attenuated/ruptured posterior tibial tendons was conducted of all patients who underwent tendon reconstruction over a 4-year period. The study comprised 20 feet in 19 patients having an average age of 53.3 years, with an average follow-up of 2 years. Preoperative magnetic resonance images were taken and graded for assignment to one of three magnetic resonance imaging (MRI)-based groups. The surgical grade was determined intraoperatively based on a previously described classification scheme. No medical or rheumatologic conditions predisposing to failure could be identified. Failure was defined as postoperative progression of pain and deformity which required subsequent triple arthrodesis. There were six failures at an average of 14.7 months. Surgical evaluation was not correlated to outcome following reconstruction. MRI grading, however, was predictive of outcome. The superior sensitivity of MRI for detecting intramural degeneration in the posterior tibial tendon that was not obvious at surgery may explain why MRI is better than intraoperative tendon inspection for predicting the outcome of reconstructive surgery. Therefore, it may be helpful to obtain preoperative MRI when this particular reconstruction of the posterior tibial tendon is contemplated, since this provides the best measure of tendon integrity and appears to be the best predictor of clinical success after such surgery.